This invention is generally directed to hydroxygallium phthalocyanines and photoconductive imaging members thereof, and more specifically the present invention is directed to processes for the preparation of hydroxygallium phthalocyanines from alkoxy-bridged gallium phthalocyanine dimers, and layered photoconductive members comprised of the aforementioned hydroxygallium phthalocyanine. The present invention in embodiments is directed to in situ processes for the preparation of hydroxygallium phthalocyanines wherein there can be avoided the use of a halo component, especially a chloro component such as chlorogallium phthalocyanine, as a precursor as it is known that such precursors can impart unfavorable properties to the aforementioned photoconductive members.
The Type V hydroxygallium phthalocyanine prepared by the processes of the present invention can be selected as photogenerator components in photoresponsive imaging members. These photoresponsive, or photoconductive imaging members may contain separate charge transport layers, especially hole transport layers containing hole transport molecules such as known tertiary aryl amines. The aforementioned photoresponsive imaging members can be negatively charged when the photogenerating layer is situated between the hole transport layer and the substrate, or positively charged when the hole transport layer is situated between the photogenerating layer and the supporting substrate. The layered photoconductor imaging members can be selected for a number of different known imaging and printing processes including, for example, electrophotographic imaging processes, especially xerographic imaging and other printing processes wherein negatively charged or positively charged images are rendered visible with toner compositions of the appropriate charge. The imaging members containing the hydroxygallium phthalocyanines are sensitive in the wavelength regions of from about 500 to about 900 nanometers, therefore, diode lasers can be selected as the light source, especially diode lasers which emit light in the region of from 700 to 850 nanometers.
In embodiments, the present invention is directed to a process for the preparation of the Type V polymorph of hydroxygallium phthalocyanine, which comprises the reaction of a gallium alkoxide with ortho-phthalodinitrile or 1,3-diiminoisoindoline, in a diol in the absence or in the presence of a solvent to obtain an alkoxy-bridged gallium phthalocyanine dimer, which dimer is hydrolyzed and converted to Type V hydroxygallium phthalocyanine. The aforementioned hydrolysis and conversion involves hydrolyzing the precursor dimer by dissolving it in a strong acid and then reprecipitating the resulting dissolved pigment in water, or an aqueous solvent, such as aqueous ammonia, thereby forming the Type I polymorph of hydroxygallium phthalocyanine; and treating the Type I hydroxygallium phthalocyanine formed with a polar aprotic organic solvent, for example N,N-dimethylformamide, N-methylpyrrolidinone, dimethylsulfoxide or pyridine to convert it to Type V hydroxygallium phthalocyanine.
The preparation of hydroxygallium phthalocyanine, and certain polymorphs of hydroxygallium phthalocyanine has been described in the literature.
In Bull. Soc. Chim. Fr., 23 (1962), there is illustrated the preparation of hydroxygallium phthalocyanine via the precursor chlorogallium phthalocyanine. The precursor chlorogallium phthalocyanine is prepared by reaction of o-Cyanobenzamide with gallium chloride in the absence of solvent. o-Cyanobenzamide is heated to its melting point (172.degree. C.), and to it is added gallium chloride, at which time the temperature is increased to 210.degree. C. for 15 minutes, and then cooled. The solid is recrystallized out of boiling chloronaphthalene, to provide purple crystals having carbon, hydrogen and chlorine analyses matching theoretical values for chlorogallium phthalocyanine. Dissolution in concentrated sulfuric acid, followed by reprecipitation in diluted aqueous ammonia affords material having carbon, and hydrogen analyses matching theoretical values for hydroxygallium phthalocyanine.
In Inorg. Chem. (19), 3131, (1980), there is illustrated the preparation of chlorogallium phthalocyanine by reaction of o-phthalodinitrile with gallium chloride in the solvent quinoline.
Further, there are illustrated in JPLO 1-221459 (Toyo Ink Manufacturing) processes for preparing chlorogallium phthalocyanines and hydroxygallium phthalocyanines, and photoreceptors for use in electrophotography comprising a charge generation material and charge transport material on a conductive substrate, and wherein the charge generation material comprises one or a mixture of two specific gallium phthalocyanine compounds.
A number of hydroxygallium phthalocyanine polymorphs and processes for the preparation thereof are described in the JPLO 5-263007, the disclosure of which is totally incorporated herein by reference. One of the polymorphs, described herein as Type V hydroxygallium phthalocyanine is described in the JPLO 5-263007 by its X-ray diffraction pattern, which shows intense diffraction peaks at Bragg angles 7.5, 9.9, 12.5, 16.3, 18.6, 21.9, 23.9, 25.1 and 28.3, with the highest peak at 7.5 degrees 2.THETA. (2 theta.+-.0.2.degree.) in the X-ray diffraction spectrum.
The Type V hydroxygallium phthalocyanine is prepared, for example, from chlorogallium phthalocyanine obtained by the reaction of gallium chloride in a solvent, such as 1-chloronaphthalene, with orthophthalodinitrile or 1,3-diiminoisoindoline, hydrolyzing the pigment precursor chlorogallium phthalocyanine by standard methods, for example acid pasting, whereby the pigment precursor is dissolved in concentrated sulfuric acid and then reprecipitated in a solvent, such as water, or a dilute ammonia solution; and subsequently treating or contacting the resulting Type I hydroxygallium phthalocyanine with a solvent, such as N,N-dimethylformamide by, for example, ball milling in the presence of spherical glass beads to provide Type V hydroxygallium phthalocyanine.
Also, in U. S. Pat. No. 5,473,064, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of Type V hydroxygallium phthalocyanine, essentially free of chlorine, whereby a chlorogallium phthalocyanine pigment precursor is prepared by reaction of gallium chloride with 1,3-diiminoisoindoline in a solvent such as N-methylpyrrolidone; hydrolyzing said pigment precursor chlorogallium phthalocyanine by, for example, dissolving the pigment precursor in concentrated sulfuric acid, and then reprecipitating in a solvent, such as water, or a dilute ammonia solution; and subsequently treating the resulting hydroxygallium phthalocyanine with a solvent, such as N,N-dimethylformamide, by for example, ball milling said hydroxygallium phthalocyanine pigment in the presence of spherical glass beads. The Type V hydroxygallium phthalocyanine obtained from the chlorogallium phthalocyanine precursor prepared according to this procedure contains very low levels of residual chlorine of from about 0.001 percent to about 0.1 percent of the weight of the Type V hydroxygailium pigment as determined by elemental analysis and can enable improved electrical performance of the Type V hydroxygallium as a photogenerating pigment, and improved desirable dark decay and cycling characteristics for the resulting photoconductive imaging member.
Further in U.S. Pat. No. 5,407,766, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of Type V hydroxygallium phthalocyanine, which comprises formation of a nonchlorinated gallium phthalocyanine precursor prepared by reaction of 1,3-diiminoisoindoline with gallium acetylacetonate in a suitable solvent; hydrolyzing the precursor by dissolving in a strong acid and then reprecipitating the dissolved pigment in aqueous ammonia, thereby forming hydroxygallium phthalocyanine; and admixing the hydroxygallium phthalocyanine with a polar aprotic organic solvent, such as N,N-dimethylformamide, to obtain Type V hydroxygallium phthalocyanine that possesses improved electrical characteristics for the Type V hydroxygallium pigment and wherein there is enabled in embodiments Type V with lower pico/seconds, improved dark decay and improved cycling characteristics for the layered imaging member thereof.
In the aforementioned documents, synthesis and processing conditions were disclosed for the preparation of hydroxygallium phthalocyanines, including Type V hydroxygallium phthalocyanine which could be used in electrophotographic applications. Complex electrophotographic properties such as photosensitivity, dark decay, cyclic stability and environmental stability of photoconductive members, or electrophotographic photoreceptors are primarily dependent on=n purity, dopants, morphology, crystal defects and analytical differences in the pigments. These differences in the electrophotographical properties of a pigment, often a particular polymorph, are usually traced to the processes by which the pigment was obtained, or to the pigment precursor used to obtain a certain polymorph.
To obtain a phthalocyanine based electrophotographic photoreceptor having high sensitivity to near infrared light, it is believed necessary to control the purity and chemical structure of the pigment, as well as to prepare the pigment in the correct crystal modification, as is generally the situation with many organic photoconductors. It is also known that certain impurities, such as ionic species, or sulfur in some situations, as well as phthalocyanine ring chlorination, even at very low levels, can be detrimental. Thus, there is a need for processes in which the pigments are obtained in high purity, acceptable yields and with superior electrophotographic properties.
In the present application, there are disclosed processes for the preparation of Type V hydroxygallium phthalocyanine using as precursor an alkoxy-bridged gallium phthalocyanine, the formula and preparation thereof being described in the copending applications. This method is an improvement over the prior art in that, for example, it does not use chlorogallium phthalocyanine as a precursor. Undesirable ring chlorination which often occurs in the preparation of chlorogallium phthalocyanine as gallium chloride is used at high temperature in the synthesis, and such chlorination can be avoided or minimized with the processes of the present invention.
In comparison, in the synthesis of an alkoxy-bridged gallium phthalocyanine dimer, gallium chloride is converted to a less-reactive gallium alkoxide prior to the phthalocyanine synthesis being performed at elevated temperature.
The alkoxy-bridged gallium phthalocyanine dimer precursor can be hydrolyzed to hydroxygallium phthalocyanine by standard methods, such as by treatment with sulfuric acid, using a procedure similar to that described for the hydrolysis of chlorogallium phthalocyanine in Bull. Soc. Chim. Fr., 23 (1962), and then converting the hydroxygallium phthalocyanine to the Type V hydroxygallium phthalocyanine polymorph, as described, for example, in JPLO 5-263007. By using an alkoxy-bridged gallium phthalocyanine dimer precursor for Type V hydroxygallium phthalocyanine, any negative effects of residual chlorine, or ring chlorination are avoided. The invention process is a high yield, high purity, and economical process for the preparation of Type V hydroxygallium phthalocyanine. Furthermore, the Type r hydroxygallium phthalocyanine obtained, according to this method, from an alkoxy-bridged gallium phthalocyanine dimer precursor, shows superior electrophotographic properties when compared to Type V hydroxygallium phthalocyanine obtained according to the prior art.
In the following patents and copending patent applications filed concurrently herewith there is illustrated: U.S. Pat. No. 5,466,796 alkoxy-bridged metallophthalocyanine dimers of the formula C.sub.32 H.sub.16 N.sub.8 MOROMN.sub.8 H.sub.16 C.sub.32, or of the formula ##STR1## wherein M is a metal, and R is an alkyl or an alkyl ether; U.S. Pat. No. 5,456,998 a photoconductive imaging member comprised of an alkoxy-bridged metallophthalocyanine dimer as a charge generator material, wherein the dimer is of the formula C.sub.32 H.sub.16 N.sub.8 MOROMN N.sub.8 H.sub.16 C.sub.32 wherein M is a trivalent metal, and R is an alkyl group or an alkyl ether group ##STR2## and U.S. Ser. No. 233,195 is a process for the preparation of alkoxy-bridged metallophthalocyanine dimers by the reaction of a trivalent metal compound with ortho-phthalodinitrile or 1,3-diiminoisoindoline in the presence of a diol.
The disclosures of all of the aforementioned publications, laid open applications, copending applications and patents are totally incorporated herein by reference.